ISOTROPIC γ-ray BACKGROUND: COSMIC-RAY INDUCED ALBEDO FROM DEBRIS IN THE SOLAR SYSTEM?

We calculate the γ-ray albedo due to cosmic-ray interactions with debris (small rocks, dust, and grains) in the Oort Cloud. We show that under reasonable assumptions a significant proportion of what is called the “extragalactic γ-ray background” could be produced at the outer frontier of the solar system and may be detectable by the Large Area Telescope, the primary instrument on the Fermi Gamma-ray Space Telescope. If detected it could provide unique direct information about the total column density of material in the Oort Cloud that is difficult to access by any other method. The same γ-ray production process takes place in other populations of small solar system bodies such as Main Belt asteroids, Jovian and Neptunian Trojans, and Kuiper Belt objects. Their detection can be used to constrain the total mass of debris in these systems. Subject headings: interplanetary medium — Kuiper Belt — Oort Cloud — cosmic rays — diffuse radiation — gamma-rays: theory